[unreadable] [unreadable] Obesity is a recently established risk factor for breast cancer incidence and mortality. To better understand the relationship between diet, obesity and mammary tumorigenesis, the Camarillo lab has developed a new rat model of early onset Diet Induced Obesity (DIO). We have shown that young female rats fed a Western Style diet have a significantly higher body fat mass and elevated serum comorbidity factors, as compared to Chow fed Lean rats. When these animals are treated with the chemical carcinogen MNU, mammary tumors appear sooner and in greater numbers in Obese rats. We determined via histology that tumors from Obese rats are of a more aggressive type compared to tumors from Lean rats. This correlates with the link between human obesity and breast cancer mortality. A major advantage of this new animal model is that mammary tumors, both low-grade and invasive hi-grade, are predictably produced. With the goal of improving methods for tumor detection, the Cheng lab is pioneering the development of Coherent Anti-Stokes Raman Scattering (CARS) microscopy, a highly sensitive noninvasive imaging technique that does not require dyes or labeling of cells. For this technique we have built a multi-modal multiphoton microscope that allows imaging of tumor cell morphology and stromal composition, valuable indicators of tumor aggressiveness. These microscopy techniques provide an excellent means to monitor mammary tumor progression in our rat model. In our recent collaborative efforts we have imaged mammary tumors and tumor-free mammary tissues. The proposed studies exploit our new imaging technologies to evaluate the influence of fatty acids (FA) on mammary tumorigenesis in our novel model of obesity and breast cancer. Recent studies suggest that type of fat consumed, but not total amount, is important towards cancer risk. We hypothesize that consumption of a diet rich in Omega-3 FA, but still high in total fat, will inhibit tumor formation and result in fewer aggressive tumors in our rat model. To test this hypothesis we will 1) optimize the multiphoton microscope for imaging of invasive and low- grade mammary tumors from Obese and Lean rats and 2) evaluate the influence of Omega-3 FA on mammary tumor formation in Obese rats fed a Western Diet. The proposed studies will establish our ability to determine tumor phenotype through advanced imaging. We will also determine the benefits of diet modification on tumor formation in a diet-induced obese population of animals. This work will lay the foundation for developing improved methods for earlier detection of aggressive tumors, for establishing dietary behaviors for cancer prevention and for better understanding the mechanisms of omega-3 FA. [unreadable] [unreadable] [unreadable]